During a tribology test, the engaging surfaces of two samples are brought in contact to measure friction and wear. In a reciprocating, rotary, fretting, or oscillating test, one of the samples may move while the other sample remains stationary. In some cases, the upper sample may be stationary while in other cases the upper sample may be moveable. The test requires applying a known force and studying the effects of force, speed, time, temperature, or other factors of friction, wear, life of coatings or bulk materials, lubricants, fluids, etc. In tribology, important parameters are load, stroke, speed, and environmental conditions.
A variety of methods and apparatuses can be used for measuring and analyzing the results of tribology tests. Such methods and apparatuses can be classified as mechanical, electrical, and optical. Each of these groups offers a different implementation. For example, a scratch test measures the adhesion or hardness of coatings or matrix materials. Typically, such a test involves moving a sharp tip for a fixed distance at a known velocity under an increasing or constant load. The final scratch marks are analyzed (during and after test) to calculate adhesion or hardness of the material. Such methods and apparatus are available in a variety of modifications, one of which is a tester coupled with an atomic force microscope.
For example, US Patent Application Publication 2015/0075264 issued in 2015 discloses an optical microscope used for pre-inspection of a subject, wherein an atomic force microscope (AFM) integrated with the optical microscope is passed over a subject and the subject surface is scanned according to the measured deflection of the AFM cantilever. A laser is directed at the cantilever, and the reflected laser light is incident on a photodiode that accordingly detects deflection of the cantilever. The AFM cantilever deflects according to one of the mechanical contact forces, van der Waals force, capillary forced, chemical bonding, electrostatic force, magnetic force, etc.
One of the advanced methods in the field of material testing is the use of confocal microscopy (see. e.g., U.S. Pat. No. 7,839,496 issued on Nov. 23, 2010 to Leonard J. Borucki). The invention relates to a sample holder for confocal microscopy of chemical mechanical polishing (CMP) pad samples cut or otherwise removed from either new or used CMP pads that maintains uniform load and pressure over the part of the sample visible to the confocal microscope.
U.S. Pat. No. 5,760,950 issued on Jun. 2, 1998 to Maly, et al, discloses a scanning confocal microscope optical system for forming an image of a subject illuminated by light from an illumination system that includes a Nipkow disk arranged perpendicular to a light propagation path and that has a surface on which a plurality of pinholes are distributed substantially symmetrically about an axis perpendicular to the surface of the disk. The system further includes components for projecting an image of a first set of pinholes onto a second set of pinholes, the image being formed of light transmitted by the first set of pinholes when the first set is illuminated by light that impinges on the first side of the disk. The system further includes a collective lens and a first objective lens for focusing light transmitted by the second set of pinholes onto the subject and for collecting light reflected by the subject. The first objective lens has a large numerical aperture. Light reflected by the subject passes through the second set of pinholes. Finally, the system may include a device for spinning the Nipkow disk about the axis.
Chinese Patent No. 102607977 B issued in 2014 describes an abrasion in-situ measuring device and a method based on digital image processing. This device comprises an attachment to a universal material tester and contains a frame attachable to the base of the tester and supporting sliders moveable in the directions of X, Y, and Z axes, one slider of which carries a digital microscope that can be used for recording the results of testing in situ and for subsequent analysis of the recorded data.
Known in the art are also tribology testers which combine determination of physical properties of the materials, e.g., by scratch testing, by using Raman spectroscopy for determination of components of the test material, etc. Although it is not strictly correct, for convenience of the description let us call such determination of test material components as determination of “chemical properties” of the test material.
For example, US Patent Application Publication No. 20160207825 A1 published on Jul. 21, 2016 (Inventors: M. Black, et al.) discloses testing of strength of a laminated material by using Raman microscope. The Raman measurements are obtained at two different wavelengths, 442 nm and 514 nm. The dominant peak observed is the “G” peak that is related to sp2 bond stretching graphitic modes in the polymeric scratch resistant layer. The Raman measurements are taken at two different wavelengths to assess the shift in the “G” peak position with excitation energy, allowing the measurement of the dispersion. The dispersion is useful in determining the atomic bonding in the polymer scratch resistant layer.
The samples are also measured to determine the thickness of a polymer scratch resistant layer using ellipsometry. The samples are also tested with a nano-indentation test using a Berkovitch diamond indenter. The Berkovitch diamond indenter is used to furrow scratches into the surface of the polymeric scratch resistant layer of each sample. In the test, the tip of the Berkovitch diamond indenter is brought into contact with the surface of the sample. One or more aspects of the disclosure pertained to a laminate including a substrate, such as a glass substrate, which may be strengthened, or a sapphire substrate, and a polymer scratch resistant layer disposed on the substrate. In one or more embodiments, where a glass substrate is utilized, the average flexural strength of the glass substrate is maintained when combined with the polymeric scratch resistant layer.
International Patent Application Publication No. WO 1996010737 A1 (issued on Apr. 11, 1996; Inventors: G. Pitt, et al.) discloses a scratch tester, in which a film or coating on a sample is scratched by a stylus in order to examine qualities such as its cohesion or adhesion to the substrate. Simultaneously or subsequently, the scratched surface is illuminated by laser light, e.g. through a microscope, in order to generate Raman scattered light. The Raman scattered light passes back through the microscope and is analyzed to determine stresses or strains present in the scratched region. This enables the determination of quantitative information about the quality of the film or coating. Similar Raman analysis methods may be used in indentation testing and tribological testing.
However, the delivered laser light and the received Raman irradiation are supplied and received through a common channel, and this involves subsequent problems in connection with separation of a useful signal from the luminescence background signal.
U.S. Pat. No. 7,944,555 B2 issued on May 17, 2011 to R. Claps relates to medical application of high-speed, rugged, time-resolved, Raman spectroscopy for sensing multiple components of a sample and for diagnostics of pathological skin conditions such as cancer. One embodiment of the device employs a rotating optical switch to time multiplex an input signal through multiple band-pass filters and into a single optical detector which is electrically activated only when the filtered input light pulse is about to impact it. Time-multiplexing the input signal through multiple optical filters and time-sequencing the optical detector enables to accelerate the analysis. One embodiment shows a system for Raman spectroscopy which employs multiple lasers, which provide signals of different wavelengths λ1, λ2, λ3, respectively. These signals are transmitted to a time-division multiplexer which has thereon an optical system which allows these signals to be transmitted in sequence to a sample. The Stokes radiation scattered from the samples sent to optical circulator and from there is sent to a notched filter that blocks the signals with wavelengths λ1, λ2, and λ3 but which passes the stokes radiation associated with these wavelengths. Optical filter, although a blocking filter for the wavelengths λ1, λ2, and λ3, is a single band-pass or band-block filter for the Stokes radiation. This combined filter is made possible by the large spectral range between the illumination radiation and the Stokes radiation in most Raman signals.
US Patent Application Publication No. 20120099102 A1 published on Apr. 26, 2012 (Inventor: J. Bello) discloses a dual and multi-wavelength sampling probe for Raman spectroscopy. The application relates to optical probes and methods for conducting Raman spectroscopy of a material at multiple excitation wavelengths. The probes and methods utilize optical elements to focus outputs from a plurality of light sources or lasers onto a sample, collect backscattered light from the sample, separate Raman spectra from the backscattered light, and provide at least one output containing the spectra. By utilizing multiple excitation wavelengths, the probes and methods avoid Raman measurement issues that may occur due to, for example, fluorescence and/or luminescence. A disadvantage of the proposed Raman sampling probe is that the excitation laser light and the received Raman radiation are delivered and received through a common channel which inevitably creates problems in subsequent separation of the signals.
However, all apparatuses for in-line testing and surface analysis of test materials with participation of Raman spectroscopy have a linear arrangement of test and measurement stations and therefore such apparatuses occupy a large floor space. Another disadvantage of linear in-line-test and surface-analysis apparatuses is that they cannot ensure high accuracy in reinstallation of the test and measurement units in the same point of interest over the test sample. On the other hand, the use of a Raman spectroscopy probe for analyzing distribution of the material components in the depth direction during wear test requires high accuracy for observing conditions of wear or destruction in the same point of interest.